P1331 - Lynch Syndrome: The Elephant in the Room

Olalekan H. Akanbi, MD, MPH, Harleen K. Chela, MBBS, MD, Veysel Tahan, MD, Ebubekir Daglilar, MD
University of Missouri, Columbia, MO

Introduction: Lynch syndrome is the most common form of hereditary colon cancer. It is caused by germline mutations in DNA mismatch repair genes (MLH1, MSH2, MSH6, PMS2, and EPCAM) leading to accelerated cancerous change in polyps and associated with development of colorectal cancer (CRC). Testing is indicated in those with (CRC), multiple primary cancer diagnoses, family history of lynch syndrome or related cancers. Advanced or recurrent large adenomas may be an indicator for hereditary cancer syndromes although routine testing in these cases is not currently widespread in clinical practice

Case Description/Methods: A 70-year-old male with a history of hypertension, basal cell skin cancer without a family history of CRC had screening colonoscopy done 6 years ago showing a total of 5 polyps including a 2cm flat polyp in the proximal ascending colon (AC) for which an endoscopic mucosal rection (EMR) was done. Pathology showed sessile serrated adenoma (SSA) without dysplasia or malignancy. Surveillance colonoscopy in 1 year revealed two 3-4mm polyps in the cecum and AC different from the site of previous EMR with pathology noting SSA. Follow-up colonoscopy in 2 years showed a proximal AC 15mm flat polyp for which another EMR was performed. Pathology of this polyp noted intramucosal carcinoma arising in the background of SSA and high-grade dysplasia involving the cauterized edges. Immunohistochemical (IHC) staining was performed for the mismatch repair proteins MLH-1, PMS-2, MSH-2 and MSH-6. Tumor cells were positive for MSH-2 and MSH-6, negative for MLH-1 and PMS-2 with the loss of staining indicating microsatellite instability concerning for Lynch syndrome. He was referred for genetic counseling and testing. A follow-up colonoscopy in 2 months noted polypoid lesion in proximal AC different from previous EMR sites, pathology reporting normal colon tissue. Biopsy of EMR sites were unremarkable. He had a surveillance colonoscopy 1 year later showing an ulcerated mass in proximal AC at site of previous EMR, pathology of invasive adenocarcinoma with identification of mismatch repair gene and BRAF mutations. He had a right hemicolectomy and adjuvant chemotherapy

Discussion: In addition to the above-stated indications for Lynch syndrome testing, patients who develop recurrent or advanced adenomas may also benefit from testing as our case highlights. IHC testing is performed to detect absence of mismatch repair proteins. Being cognizant of the possibility of Lynch syndrome and testing in these scenarios is important


Disclosures:


Olalekan H. Akanbi, MD, MPH, Harleen K. Chela, MBBS, MD, Veysel Tahan, MD, Ebubekir Daglilar, MD. P1331 - Lynch Syndrome: The Elephant in the Room, ACG 2021 Annual Scientific Meeting Abstracts. Las Vegas, Nevada: American College of Gastroenterology.